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U.  S.  DEPARTMENT   OF  AGRICULTURE, 

BUREAU  OF  ENTOMOLOGY— BULLETIN  No.  109,  Part  V. 

L.  O.  HOWARD,  Entomologist  and  Chief  of  Bureau. 


PAPERS  ON  INSECTS  AFFECTING  VEGETABLES. 


ARSENITE  OF  ZINC  AND  LEAD  CHRO 

MATE  AS  REMEDIES  AGAINST  THE 

COLORADO  POTATO  BEETLE. 


FEED  A.  JOHNSTON, 

Entomological  Assistant. 
[In  cooperation  with  the  Virginia  Truck  Experiment  Station.] 


Issued  April  5,  1912. 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1912. 


BUREAU  OF  ENTOMOLOGY. 

L.  0.  Howard,  Entomologist  and  Chief  of  Bureau. 

C.  L.  Marl  att,  Entomologist  and  Acting  Chief  in  Absence  of  Chief . 

R.  S.  Clifton,  Executive  Assistant. 

W.  F.  Tastet,  Chief  Clerk. 

F.  H.  Chittenden,  in  charge  of  truck  crop  and  stored  product  insect  investigations. 

A.  D.  Hopkins,  in  charge  of  forest  insect  investigations. 

W.  D.  Hunter,  in  charge  of  southern  field  crop  insect  investigations. 

F.  M.  Webster,  in  charge  of  cereal  and  forage  insect  investigations. 

A.  L.  Quaintance,  in  charge  of  deciduous  fruit  insect  investigations. 

E.  F.  Phillips,  in  charge  of  bee  culture. 

D.  M.  Rogers,  in  charge  of  preventing  spread  of  moths,  field  work. 

Rolla  P.  Currie,  in  charge  of  editorial  work. 

Mabel  Colcord,  in  charge  of  library. 

Truck  Crop  and  Stored  Product  Insect  Investigations. 

F.  H.  Chittenden,  in  charge. 

H.  M.  Russell,  C.  H.  Popenoe,  Wm.  B.  Parker,  H.  0.  Marsh,  M.  M.  High, 

Fred  A.  Johnston,  John  E.  Graf,  entomological  assistants. 
I.  J.  Condit,  collaborator  in  California. 
P.  T.  Cole,  collaborator  in  tidewater  Virginia. 
W.  N.  Ord,  collaborator  in  Oregon. 
Thos.  II.  Jones,  collaborator  in  Porto  Rico. 
Marion  T.  Van  Horn,  Pauline  M.  Johnson ,preparators. 


CONTENTS 


Page. 
Spraying  experiments  with  arsenite  of  zinc  and  lead  chromate  in  comparison 

with  other  arsenicals 53 

Spraying  experiments  with  arsenite  of  zinc  at  different  strengths 55 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  Florida,  George  A.  Smathers  Libraries  with  support  from  LYRASIS  and  the  Sloan  Foundation 


http://archive.org/details/insect11fred 


U.  S.  D.  A.,  B.  E.  Bui.  109,  Part  V.  T.  C.  &  S.  P.  I.  I.,  April  5,  101: 

PAPERS  ON  INSECTS  AFFECTING  VEGETABLES. 


ARSENITE  OF  ZINC  AND  LEAD  CHROMATE  AS  REMEDIES 
AGAINST  THE  COLORADO  POTATO  BEETLE. 

By  Fred  A.  Johnston,  Entomological  Assistant. 

[In  cooperation  with  the  Virginia  Truck  Experiment  Station.] 

SPRAYING  EXPERIMENTS  WITH  ARSENITE   OF  ZINC  AND   LEAD 
CHROMATE  IN  COMPARISON  WITH  OTHER  ARSENICALS. 

In  May,  1911,  a  series  of  experiments  for  comparing  the  insecti- 
cidal  value  of  arsenite  of  zinc  and  of  Jead  chromate  with  that  of  other 
arsenicals  in  controlling  the  Colorado  potato  beetle  (Leptinotarsa 
decemlineata  Say)  was  undertaken  under  the  direction  of  Dr.  F.  H. 
Chittenden  at  the  Virginia  Truck  Experiment  Station,  at  Norfolk,  Va. 

The  season  was  later  than  usual,  making  it  unnecessary  to  spray  for 
the  potato  beetle  until  about  May  9.  At  this  date  no  larvae  were 
present  on  the  plants,  though  beetles  and  egg  masses  were   abundant. 

On  May  9  six  plats  were  sprayed.  Table  I  gives  the  insecticides 
and  strengths  used. 

Table  I. — Sprays  used  against  the  Colorado  potato  beetle,  Norfolk,  Va.,  May,  1911. 


Plat 
No. 


Insecticide  used. 


I 

II 

III 

IV 

V 

VI 


Lime-sulphur,  2  pounds  to  50  gallons  of  water  and  3  pounds  of  arsenate  of  lead. 

Arsenate  of  lead,  3  pounds  to  50  gallons  of  water. 

Lead  chromate,  2  ounces  to  4  gallons  of  water. 

Arsenite  of  zinc,  1 J  pounds  to  50  gallons  of  water. 

Bordeaux  mixture  (4-6-50  formula)  and  1J  pounds  of  Paris  green. 

Bordeaux  mixture  (4-6-50  formula)  and  if  pounds  of  arsenite  of  zinc. 


On  May  22  all  of  the  potatoes  were  resprayed,  the  same  proportions 
of  the  different  materials  being  used  with  the  exception  of  the  lead 
chromate  in  which  case  the  strength  was  doubled.  (One  ounce  to  a 
gallon  of  water.) 

At  this  date  the  larvae  were  exceedingly  numerous  and  doing  much 
damage  in  unsprayed  potato  fields. 

21142°— 12  53 


54 


PAPEBS  ON  INSECTS  AFFECTING  VEGETABLES. 


On  the  day  following  the  second  application  of  the  sprays  a  count 
of  the  infested  plants  in  each  plat  was  made  and  the  following  figures 
obtained: 

Table  II. — Results  of  spray  applications  against  the  Colorado  potato  beetle,  Norfolk, 

Va.,  May,  1911. 


Plat 
No. 


Insecticide  used. 


Number 

Number 

of  in- 

of un  in- 

fested 

fested 

plants. 

plants. 

37 

347 

118 

622 

216 

169 

206 

1,048 

152 

741 

225 

555 

Infesta- 
tion. 


I 

II 

III 

IV 
V 

VI 


Lime-sulphur  (2-50  formula)  and  3  pounds  of  arsenate  of  lead 

Arsenate  of  lead,  3  pounds  to  50  gallons  of  water 

Lead  chromate,  2  ounces  to  4  gallons  of  water,  and  1  ounce  to  1  gal 

Ion  of  water 

Arsenite  of  zinc,  1 J  pounds  to  50  gallons  of  water 

Bordeaux  mixture  (4-6-50  formula)  and  1J  pounds  Paris  green 

Bordeaux  mixture  (4-6-50  formula)  and  1§  pounds  arsenite  of  zinc. . 


Per  cent. 
9.6 
15.9 

+56.0 
16.4 

+  17.0 
28.8 


It  will  be  seen  that  the  results  obtained  from  the  use  of  lead 
chromate  were  very  unsatisfactory  as  compared  with  those  in  the 
case  of  other  insecticides  used.  The  lead  chromate  employed  was  in 
the  form  of  a  powder,  and  great  difficulty  was  experienced  in  making 
it  mix  well  with  water,  it  having  a  tendency  to  settle  quite  rapidly, 
requiring  constant  agitation  to  keep  it  in  solution.  It  adhered  well 
to  the  foliage,  and  its  color  stood  out  quite  prominently  in  contrast 
to  the  other  plats.  However,  the  young  larvae  seemed  to  be  able  to 
feed  on  plants  that  were  thoroughly  covered  with  the  material  without 
receiving  much  injury. 

The  arsenite  of  zinc  employed  was  also  in  the  powdered  form.  It  is 
much  lighter  than  lead  chromate  and  remains  in  suspension  in  water 
much  better.  It  adheres  to  the  foliage  very  well  and  does  not,  so  far 
as  could  be  observed,  burn  or  injure  the  plants  in  any  way. 

The  percentage  of  infested  plants  in  the  plat  that  was  treated 
with  Bordeaux  mixture  and  arsenite  of  zinc  was  somewhat  greater 
than  in  the  plat  in  which  the  arsenite  of  zinc  alone  had  been  used. 
This  was  no  doubt  due  partly  to  the  fact  that  the  Bordeaux-arsenite 
of  zinc  plat  was  in  a  different  field,  one  which  had  been  in  potatoes  the 
previous  year  and  was  thus  subject  to  the  attack  of  a  greater  number 
of  beetles.  Also,  many  of  the  plants  which  were  counted  as  infested 
were  only  slightly  injured,  and  it  is  doubtful  if  the  yield  of  potatoes 
would  have  been  much  lessened. 

On  June  29  the  potatoes  were  dug,  and  following  are  the  weights 
of  one  row  of  potatoes  in  each  of  the  first  four  plats. 


AESENITE    OF   ZINC    AGAINST   POTATO    BEETLE. 


55 


Table  III. —  Yields  of  potatoes  from  one  row  from  each  of  Plats  I,  II,  III,  and  IV 
sprayed  as  indicated  in  Table  I. 


One 
row 
from 
plat 
No. 


I 

II 
III 
IV 


Insecticide  used. 


Lime-sulphur  and  arsenate  of  lead 

Arsenate  of  lead 

Lead  chromate 

Arsenite  of  zinc 


Number 
of  plants 
in  row. 


Weight  Weight 
of  No.  1  of  No.  2 
potatoes.1  potatoes. 


Pounds. 

384 

188J 

3G8 

172f 

385 

128 

374 

143J 

Pounds. 
25 1 
26 
19J 
18 


1  Excellent  to  good. 


2  Fair  to  indifferent. 


By  taking  the  yield  of  the  same  number  of  plants  from  each  row  the 
contrast  between  the  different  rows  will  be  more  marked.  Table  IV 
represents  the  yield  of  374  plants  from  each  row: 

Table  IV. —  Yields  of  potatoes  from  374  plants  from  one  row  from  each  of  Plats  I,  II, 
III,  and  IV,  sprayed  as  indicated  in  Table  I. 


One 
row 
from 
plat 
No. 


I 

II 
III 
IV 


Insecticide  used. 


Lime-sulphur  and  arsenate  of  lead 

Arsenate  of  lead 

Lead  chromate 

Arsenite  of  zinc 


Number 

Weight 

of  plants 

of  No.  1 

m  row. 

potatoes.1 

Pounds. 

374 

183.26 

374 

175.  401 

374 

124. 168 

374 

143.5 

Weight 
of  No.  2 
potatoes.2 


Pounds. 
25.05 
26.18 
19.07 
18 


Excellent  to  good. 


2  Fair  to  indifferent. 


SPRAYING  EXPERIMENTS  WITH  ARSENITE  OF  ZINC  AT  VARIOUS 

STRENGTHS. 

An  experiment  with  the  three  following  strengths  of  arsenite  of 
zinc  in  controlling  the  Colorado  potato  beetle  was  begun  at  the  Vir- 
ginia Truck  Experiment  Station,  Norfolk,  Ya.,  on  May  31,  1911. 

No.  I,  arsenite  of  zinc,  1  pound  to  50  gallons  of  water. 
No.  II,  arsenite  of  zinc,  1|  pounds  to  50  gallons  of  water. 
No.  Ill,  arsenite  of  zinc,  2  pounds  to  50  gallons  of  water. 

On  the  day  the  spraying  was  done  (May  31)  the  rows  sprayed  with 
No.  I,  No.  II,  and  No.  Ill  had  47,  86,  and  88  infested  plants,  respec- 
tively. 

On  June  2  the  row  treated  with  No.  I  had  33  infested  plants,  a 
decreased  infestation  of  14  plants,  or  29.8  per  cent.  The  row  treated 
with  No.  II  had  57  infested  plants,  a  decreased  infestation  of  29 
plants,  or  33.7  per  cent,  while  the  row  treated  with  No.  Ill  had  38 
infested  plants,  a  decreased  infestation  of  50  plants,  or  56.8  per  cent. 


UNIVERSITY  OF  FLORIDA 


56 


PAPERS  ON  ENSECTS  AFFECTING 


3  1262  08928  8509 

On  June  3  the  count  was  again  taken,  and  the  row  treated  with  Xo. 
I  had  15  infested  plants,  a  decreased  infestation  of  32  plants,  or  68  + 
per  cent.  The  row  treated  with  Xo.  II  had  23  infested  plants,  a 
dec  leased  infestation  of  63  plants,  or  73.2  per  cent,  while  the  row 
treated  with  Xo.  Ill  had  13  infested  plants,  a  decreased  infestation  of 
75  plants,  or  85.2  per  cent. 

The  following  table  shows  the  number  of  infested  plants  in  the 
plats  before  and  after  spraying: 


Table  V 


-Results  of  applications  of  arsenite  of  zinc  at  different  strengths  against  the 
Colorado  potato  beetle. 


Date. 

Solu- 
tion 
Xo. 

Number  of 
infested 
plants. 

Decrease  in 

number  of 

infested 

plants. 

Decrease  of 
infesta- 
tion. 

1911. 
May  31 

I 

II 
III 

47 
86 
88 
33 
57 
38 
15 
23 
13 

Per  cent. 

Do 

Do 

June  2 

I 

II 

III 

I 

II 
III 

14 
29 
50 
32 
63 
75 

29  8 

Do 

Do 

June  3 

Do 

Do 

33.7 
56.8 
68+ 
73.2 
85.2 

On  June  3  the  number  of  larvae  on  the  plants  which  were  still 
infested  was  much  smaller  than  the  number  present  when  the  spray 
was  first  applied.  The  extent  of  infestation  of  some  plants  amounted 
to  but  one  or  two  larvae;  these  plants,  however,  were  counted  in  as 
infested. 

Results. — From  the  preceding  table  it  will  be  seen  that  far  better 
results  were  obtained  where  2  pounds  of  arsenite  of  zinc  to  50  gallons 
of  water  were  used. 

The  results  were  obtained  more  quickly,  and  a  larger  percentage  of 
larvae  was  killed.  At  this  strength  arsenite  of  zinc  did  not  burn  or 
injure  the  foliage  in  any  way,  and  without  doubt  an  even  greater 
amount  of  the  arsenical  might  be  used  without  injury  to  the  plants 
and  with  correspondingly  greater  efficiency  in  killing  the  beetles. 


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